What a MET is and why the calculation uses oxygen
A MET — metabolic equivalent of task — expresses the energy cost of an activity as a multiple of resting metabolism. By convention, one MET is 3.5 millilitres of oxygen consumed per kilogram of body weight per minute. Cycling at 12 to 14 mph is rated 8 METs, so it costs eight times the resting rate: 28 mL of oxygen per kilogram per minute.
Oxygen is the currency because it is what exercise physiologists can actually measure. Put a mask on someone, measure the oxygen they take in and the carbon dioxide they breathe out, and you have their energy expenditure directly, because burning fuel in the body consumes oxygen in a nearly fixed ratio to the energy released. For a mixed diet, one litre of oxygen corresponds to about 5 kilocalories.
That is where the 200 in the formula comes from. Multiply MET by 3.5 to get millilitres per kilogram per minute, multiply by body weight to get millilitres per minute, divide by 1,000 to get litres, and multiply by 5 to get kilocalories. Dividing by 1,000 and multiplying by 5 is the same as dividing by 200, so the whole chain collapses to MET × 3.5 × kg ÷ 200.
The MET values themselves come from the Compendium of Physical Activities, compiled by Ainsworth and colleagues and revised in 2011. It lists hundreds of activities with a code and a MET value, each drawn from measured oxygen uptake studies where those exist and estimated where they do not.
Gross calories, net calories, and which one you want
The formula gives you gross energy cost — everything you spent during the session, including the resting metabolism you would have spent lying on the sofa. The net figure subtracts that baseline by using MET − 1 instead of MET.
The difference is not trivial for low-intensity activity. An hour of walking at 3.5 METs for an 80 kg person costs 294 kcal gross but only 210 kcal net, because 84 kcal of that hour was resting metabolism. At 9.8 METs the same 84 kcal is a much smaller share: 823 kcal gross against 739 kcal net for the same person and duration.
Which figure you want depends on what you are doing with it. If you are simply asking what a workout cost, the gross figure is the natural answer. If you are subtracting exercise from a calorie budget built on a total daily expenditure estimate — as in the TDEE calculator — you must use the net figure, because your TDEE already includes resting metabolism for all 24 hours. Adding gross exercise calories on top double-counts the baseline, and that error is one of the more common reasons a food-tracking app's daily budget drifts upward faster than the training justifies.
Worked example: 35 minutes of running at 6 mph, body weight 82 kg
Running at 6.0 mph — a ten-minute mile — is 9.8 METs in the Compendium.
- Oxygen cost. 9.8 × 3.5 = 34.3 mL of oxygen per kilogram per minute.
- Energy rate. 9.8 × 3.5 × 82 ÷ 200 = 2,812.6 ÷ 200 = 14.06 kcal per minute.
- Gross total. 14.06 × 35 = 492 kcal.
- Net above rest. (9.8 − 1) × 3.5 × 82 ÷ 200 = 12.63 kcal per minute, so 12.63 × 35 = 442 kcal.
Check the sensitivity to weight, because it is exactly linear: a 100 kg runner doing the identical session burns 492 × 100 ÷ 82 = 600 kcal gross. Nothing about the pace changed; there is simply more mass to carry.
Compare that with an hour of brisk walking at 5.0 METs for the same 82 kg person: 5.0 × 3.5 × 82 ÷ 200 = 7.175 kcal/min, or 431 kcal in sixty minutes. The 35-minute run beats a 60-minute walk on total energy — but the walk is far easier to repeat daily, which is why weekly volume usually matters more than the intensity of any single session.
If you are converting this into a weight-loss timeline, 442 net kcal three times a week is 1,326 kcal, roughly 0.17 kg of body fat a week from training alone. Put that alongside a dietary deficit in the calorie deficit calculator to see the combined rate.
How much to trust the number
Treat MET estimates as accurate to within roughly a tenth to a fifth of the value, not to the calorie. Three separate sources of error stack up.
The 3.5 mL/kg/min definition is a convention, not a measurement of you. Measured resting oxygen uptake is lower than 3.5 for a large share of adults, and the gap is bigger for people who are older, heavier or carrying more fat, because fat mass consumes little oxygen but still counts in the per-kilogram denominator. Where this matters, MET-based figures run high.
Compendium values are population averages for a described intensity. Two people both "cycling 12 to 14 mph" can differ substantially in efficiency, terrain and wind. The value is right for the activity as defined, not for your execution of it.
Duration is usually overstated. A "one-hour" gym session rarely contains sixty minutes at the target intensity. Enter time actually spent working, not time elapsed.
What the method is genuinely good at is comparison. The ratio between two activities is far more reliable than either absolute figure, so use it to decide whether to swim or cycle, and use the scale over several weeks to calibrate what your training is actually worth.
Calories in 30 minutes by activity and body weight
| Activity | MET | 70 kg (154 lb) | 90 kg (198 lb) |
|---|---|---|---|
| Walking, 3.0 mph, level | 3.5 | 129 kcal | 165 kcal |
| Walking, 4.0 mph, brisk | 5.0 | 184 kcal | 236 kcal |
| Swimming laps, moderate | 5.8 | 213 kcal | 274 kcal |
| Resistance training, vigorous | 6.0 | 221 kcal | 284 kcal |
| Rowing ergometer, moderate | 7.0 | 257 kcal | 331 kcal |
| Bicycling, 12–13.9 mph | 8.0 | 294 kcal | 378 kcal |
| Running, 6.0 mph | 9.8 | 360 kcal | 463 kcal |
| Running, 8.0 mph | 11.8 | 434 kcal | 558 kcal |
The two weight columns differ by exactly the ratio 90 ÷ 70 = 1.286, because energy cost is linear in body weight.
Mistakes that make the estimate wrong
- Counting gross calories against a TDEE budget. Your total daily expenditure already contains resting metabolism for the whole day. Subtract the net figure, not the gross one.
- Entering elapsed time instead of working time. Rest between sets, waiting at traffic lights and stopping to talk are not at the MET value you selected.
- Using a running MET at walking pace, or vice versa. The Compendium's speed brackets are narrow for a reason; the energy cost of running rises steeply with pace.
- Assuming resistance training burns like cardio. Vigorous free-weight training is rated 6.0 METs, and most of a session is rest. The value of lifting during a deficit is lean-mass retention, not the calorie burn.
- Adding an afterburn effect on top. Excess post-exercise oxygen consumption is real but modest for most sessions, and Compendium values do not include it. Adding a large EPOC bonus on top is double-counting a small effect.
- Forgetting that the number falls as you lose weight. The same run at 75 kg costs less than at 90 kg, in exact proportion.
Why fitness trackers and this calculator disagree
A wrist tracker estimates energy expenditure from heart rate, motion and your entered profile, then applies its own proprietary model. This calculator applies a published steady-state MET value. They will differ, sometimes by a lot, and neither is measuring your oxygen uptake. The MET route has the advantage that you can see exactly what it assumed and reproduce it by hand.
Where MET values come from and what else they are used for
The Compendium of Physical Activities began in 1993 to give epidemiologists a standard way to code physical activity in questionnaires. Each activity carries a five-digit code and a MET value, so that a survey answer such as "gardening for two hours a week" can be turned into an energy figure comparable across studies. That origin explains both its breadth and its limits: it was built for population research, not for individual precision.
The same MET scale underpins public-health guidance. Activity is often described as moderate at 3 to 6 METs and vigorous at 6 METs and above, and the widely cited target of 150 minutes of moderate activity a week is defined on that scale. Vigorous activity counts double, which is exactly the ratio the MET values imply.
METs also connect to aerobic fitness. Because one MET is 3.5 mL/kg/min, a VO₂ max of 42 mL/kg/min is 12 METs — meaning the highest intensity that person can sustain briefly is twelve times rest, and comfortable steady work sits well below it. That is why the same 8 MET bike ride is easy for one person and a hard session for another.
To put an activity total to use, pair it with a maintenance figure from the BMR calculator and a target from the macro split calculator, and remember that the exercise line is usually the smallest of the three terms in a day's energy balance.